The present invention relates to flame retardant resin compositions that do not produce harmful gases such as hydrogen halide when burned and have excellent mechanical strength and relates to products made by using the same, including insulated wire, tube. heat-shrinkable tube, flat cable, and high voltage DC electric wire.
The insulation of insulated wires used in the field of electronic appliances and vehicles, insulators for tubes, heat-shrinkable lubes, and flat cables, and the insulation and sheath of high voltage DC electric wires for television sets, electromagnetic cooking ranges, copying machines, and the like are generally required to have a mechanical strength of 1.0 kg/mm2 or more in terms of tensile strength. For example, referring to the UL Standards widely adopted in the field of electronic appliances, in the case of insulated wires, tubes, heat-shrinkable tubes, and flat cables using such plastics as polyethylene as the insulator, the insulator is required to have a tensile strength of 1.06 kg/mm2 or more.
Further, flame retardance is also required of the insulated wires, tubes, heat-shrinkable tubes, flat cables, and the high voltage DC electric wires used in the above fields. Generally, horizontal flame retardance of the same is required in the field of vehicles and vertical flame retardance in the field of electronic appliances.
As a method for testing the vertical flame retardance, the vertical test (VW-1 test) provided in Subject 758 of the UL Standards as shown, for example, in FIG. 1, is well known. This is a combustion test performed on a specimen 5 of an insulated wire, a tube, a heat-shrinkable tube, a flat cable, or a high voltage DC electric wire vertically held by a fastener 3. In the test, the flame of a burner 2 is applied to the same specimen five times from under the specimen for a duration of 15 seconds each time with 15 seconds intervals between the respective applications thereof In the test, it is required that the insulation cease to flame within 60 seconds, absorbent cotton 4 placed thereunder should not ignite from burning droppings from the specimen, and kraft paper 1 fixed above the specimen should not burn or scorch.
In the case of a tube, an all-tubing flame test is sometimes performed to assess the flame retardance of the specimen, namely, a metallic bar with the same diameter as the inner diameter of the tube is inserted through the tube and the specimen is subjected to the same test as the VW-1 test. Sometimes, a heat-shrinkable tube is also subjected to an all-tubing flame test to assess its flame retardance, namely, the heat-shrinkable tube is put on a metallic bar having the same diameter as the inner diameter of the heat-shrinkable tube when it becomes shrunken and the same test as the VW-1 test is performed on the specimen.
As materials for the above-described insulators of insulated wires, tubes, heat-shrinkable tubes, and insulators of flat cables satisfying the requirements for both mechanical strength and flame retardance, resin compositions comprising polyvinyl chloride such as flexible polyvinyl chloride compositions have long been known. Since such materials are excellent in both mechanical strength and flame retardance and, economical as well, they are widely used as the materials for forming insulated wires and flat cables applicable to the fields of electronic appliances and vehicles.
However, the resin compositions produced by using polyvinyl chloride generate combustion gases harmful to the human body, such as hydrogen chloride, once burned, and also many of the resin compositions are mixed with heavy metal substances such as lead-based compounds for stabilizing their processing. Hence, they have an undesirable aspect against protection of the environment.
In view of these problems, there have been known and put to practical use flame retardant resin compositions obtained by mixing ethylene polymer such as polyethylene with a phosphorus-containing flame retardant agent, or by mixing the same with a flame-retardant agent such as aluminum hydroxide or magnesium hydroxide, i.e., the so-called non-halogen flame retardant resin compositions. However, there have been problems with some of the phosphorus-containing flame-retardant agents in that they exhibit acute toxicity when taken by mouth and, further, they corrode the conductors when mixed in resin compositions used in insulated wires and flat cables.
On the other hand, flame-retardant agents made of metal hydroxide have only a moderate flame-retardant effect on such plastics as ethylene polymer. Therefore, in order to obtain flame retardance equivalent to that of the polyvinyl chloride resin composition, it is required, for example, to have 100 parts or more by weight of metal hydroxide compounded with 100 parts by weight of ethylene polymer such as polyethylene, though this is not always true because it depends on the shape and size of the product. The drawback of compounding such a large quantity of metal hydroxide with the base resin, however, is that it markedly lowers the mechanical strength of the resin composition.
Insulated wires based on the UL Standards to be used for wiring work within electronic appliances are normally prescribed to have a minimum thickness of 0.15 mm at 30 V rating, 0.4 mm at 300 V rating, and 0.8 mm at 600 V rating. Further, it is preferred that the insulated wire to be used for wiring work within electronic appliances have as small an outer diameter of as possible to allow easy handling of the wire, and for the conductor, a diameter of about 1.0 mm or less is used except in special cases (refer to page 13 of xe2x80x9cHandbook of Electronic Wire Productsxe2x80x9d, published by Sumitomo Electric Industries, Ltd.).
Halogen-free polyolefin insulated wires having a conductor of 1.0 mm or less in outer diameter and an insulation of 0.1 mm to 1.0 mm thickness which pass the VW-1 test and satisfy the requirements for mechanical strength such as initial tensile strength have been unknown. Recently, however, a thin-wall high-strength non-halogen insulated wire satisfying the UL Standards was developed (Japanese Patent Nos. 2525982 and 2525968).
Although the above-mentioned insulated wire satisfies the requirement to cease to flame within 60 seconds as provided in the Standards for the VW-1 test, it occasionally continues burning over 20 seconds. Therefore, the development of a non-halogen flame retardant insulated wire with greater flame retardance has been desired.
On the other hand, in the case of high voltage DC electric wire, ethylene-xcex1-olefin copolymer such as polyethylene is used to cover the conductor to improve the anti-tracking property of the wire. However, to offset the drawback of inflammability of polyethylene, it has been the practice to cover the high voltage DC electric wire with a flame retardant resin composition having, as the main ingredients, a halogen-containing polymer such as polyvinyl chloride, thereby securing the flame retardance of the high voltage DC electric wire. However, since the resin composition using polyvinyl chloride generates combustion gases harmful to the human body such as hydrogen chloride, once burned, and many of the resin compositions contain heavy metal substances such as a lead-base compound for the purpose of stability in the fabrication, it has an undesirable aspect from the viewpoint of environmental preservation. Therefore, the development of a non-halogen high voltage DC electric wire has been desired.
Through various investigations on the above enumerated problems, the inventors have learned that a flame retardant resin composition obtained by having 100 parts by weight of thermoplastic resin compounded with 100 to 250 parts by weight of metal hydroxide and either 5 to 50 parts by weight of acetate or 5 to 80 parts by weight of calcium carbonate does not generate harmful gases such as hydrogen halide, e.g., hydrogen chloride when burned, exhibits flame retardance of the same level or higher than that of PVC in the VW-1 test according to the UL Standards. Though the flame retardant resin composition compounded with acetate or calcium carbonate does not show a difference in terms of the limiting oxygen index (LOI) when compared with a flame retardant resin composition not compounded with acetate or calcium carbonate, it exhibits excellent mechanical strength. The inventors have confirmed that this flame retardance resin composition can be used for flame retardant insulated wire, flat cable, and high-voltage DC electric wire.
(1) Namely, the invention provides a flame retardant resin composition obtained by comprising 100 to 250 parts by weight of metal hydroxide and either 5 to 50 parts by weight of acetate or 5 to 80 parts by weight of calcium carbonate, based upon 100 parts by weight of thermoplastic resin.
(2) The flame retardant resin composition is characterized also in that it comprises the calcium carbonate in the amount from 5 to 30 parts by weight.
(3) The flame retardant resin composition is characterized in that the thermoplastic resin is one kind or a mixture of two or more kinds of ethylene-xcex1-olefin copolymer selected from ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-methacrylic acid copolymer, and ethylene-methyl acrylate copolymer.
(4) The flame retardant resin composition is characterized in that the ethylene-xcex1-olefin copolymer is an ethylene-vinylacetate copolymer containing 6 to 50 % by weight of vinyl acetate component and has a melt flow rate of 0.5 to 30(at a temperature of 190xc2x0 C. and under a load of 2.16 kg).
(5) The flame retardant resin composition is characterized in that an organosilicon compound coupling agent expressed as general formula [1]: 
(where R denotes alkyl including acryl, methacryl, or allyl and Y 1, Y 2, and Y3 denote atomic groups selected from the groups of alkyl, alkoxyl, and halogen) in the amount of 0.1 to 10 parts by weight is added to 100 parts by weight of the ethylene-xcex1-olefin copolymer.
(6) The flame retardant resin composition is characterized in that the acetate is one kind or a mixture of two or more kinds, having a particle diameter of 0.5 to 5 xcexcm, selected from magnesium acetate, sodium acetate, potassium acetate, zinc acetate, copper acetate, ferrous acetate, calcium acetate, aluminum acetate, nickel acetate, cobalt acetate, gallium acetate, silver acetate, tin acetate, barium acetate, cerium acetate, lead acetate, and beryllium acetate.
(7) The flame retardant resin composition is characterized in that the primary particle diameter of the calcium carbonate is not greater than 4 xcexcm.
(8) The flame retardant resin composition is characterized in that the calcium carbonate is one kind or a mixture of two or more kinds selected from calcium carbonate with its surface treated with a surface treatment agent such as a fatty acid type, oil and fat type, surface-active agent type, or wax type, or calcium carbonate with its surface treated with a coupling agent such as a silane type, titanate type, aluminum type, zirco-aluminum type, carboxylic acid type, or phosphate type.
(1) The invention provides an insulated wire having an insulation layer made of any of the flame retardant resin composition described in [I], (1) to (8), above.
(2) The insulated wire is characterized in that the insulation is cross-linked.
(3) The invention provides a thin-wall high-strength insulated wire having its conductor, whose outer diameter is 1.0 mm or less, covered with the flame retardant resin composition according to any of [I], (1) to (8), above to a thickness of from 0.1 mm to not greater than 1.0 mm and having the insulation cross-linked.
(1) The invention provides an insulating tube obtained by extrusion molding the flame retardant resin composition according to any of [I], (1) to (8), above into a tubular form.
(2) The tube is characterized in that the tube layer is cross-linked.
(3) The invention provides a heat shrinkable tube obtained, after a tube-formed molding made of the flame retardant resin composition according to any of [I], (1) to (8), above has been cross-linked, by expanding the tube-formed molding in its radial direction under a heated condition and, thereupon, cooling the expanded tube to fix its form.
(1) The invention provides a flat cable with a parallel arrangement of a plurality of spaced-apart conductors enclosed in an insulating layer, which is made of the flame retardant resin composition according to any of [1], (1) to (8), above.
(2) The flat cable is characterized in that the insulating layer is cross-linked.
(3) The flat cable is characterized in that at least one face of the insulating layer is laminated with a film made of a polymeric material.
(4) The flat cable is characterized in that the insulating layer is irradiated with ionizing radiation.
(1) The invention provides a high-voltage DC electric wire having its conductor provided thereon, as an insulating layer, with a coating of an ethylene-xcex1-olefin copolymer resin composition and having the insulating layer provided thereon with a jacketing made of the flame retardant resin composition according to any of [1], (1) to (8), above.
(2) The high-voltage DC electric wire is characterized in that the insulating layer and jacketing are cross-linked.
Functions performed by the above-described aspects of the invention will be summarized as follows.
The flame retardant resin composition obtained by having 100 parts by weight of thermoplastic resin compounded with 100 to 250 parts by weight of metal hydroxide and either 5 to 50 parts by weight of acetate or 5 to 80 parts by weight of calcium carbonate does not generate harmful gases such as hydrogen halide, e.g., hydrogen chloride when burned, exhibits flame retardance of an equivalent or higher level than that of PVC in the VW-1 test according to the UL Standards, and performs with excellent mechanical strength and, further, it can be used for flame retardant insulated wire, flat cable, and high-voltage DC electric wire.
By having a conductor coated with the flame retardant resin, a flame retardant insulated wire excellent in mechanical strength can be obtained.
By cross-linking the insulated wire, especially by irradiating it with ionizing radiation, an insulated wire and a flat cable excellent not only in flame retardance and mechanical strength but also in such properties as heat resistance, resistance to heat deformation, and resistance to chemicals can be obtained.
Such an insulated wire when cross-linked, even if the wire is of a structure having a thin-wall insulating coating applied on an extra fine conductor, can provide a non-halogen insulated wire exhibiting high strength and high flame retardance.
The flame retardant resin composition can be molded into a tubular form to provide an insulating tube.
The insulating tube that is cross-linked exhibits properties excellent not only in flame retardance and mechanical strength but also in such properties as heat resistance, resistance to heat deformation, and resistance to chemicals.
Such a tubular molding when cross-linked, especially radiated with ionizing radiation, and then processed to expand its diameter and keep its expanded form can be made into a heat-shrinkable tube excellent in flame retardance and mechanical strength.
The flame retardant resin composition extruded to cover up both faces of parallel conductors formed by conductors arranged in parallel can provide a flame retardant flat cable excellent in mechanical strength.
The flat cable when cross-linked, especially radiated with ionizing radiation, can be made into a flat cable excellent not only in flame retardance and mechanical strength but also in such properties as heat resistance, resistance to heat deformation, and resistance to chemicals.
When the flame retardant resin composition is extruded by a melt-extruding method or the like onto one surface of a biaxially stretched polyester film to provide a laminated tape and two sheets of such laminated tape are placed on both faces of parallel conductors such that the resin composition layer is inside of the polyester film, thus forming an insulation of the parallel conductors by using a heat laminator, a flame retardant flat cable excellent in mechanical strength can be provided.
In this case, when the flat cable is cross-linked, especially irradiated with ionizing radiation, a flat cable excellent not only in flame retardance and mechanical strength but also in such properties as heat resistance, resistance to heat deformation, and resistance to chemicals can be provided.
By extruding an ethylene-xcex1-olefin copolymer resin composition as an insulation layer on a conductor and then extruding thereon the flame retardant resin composition as a jacketing, a flame retardant high-voltage DC electric wire excellent in mechanical strength and environmentally safe can be produced.
The high-voltage DC electric wire, when the insulation layer and the jacketing are cross-linked, and especially when they are irradiated by ionizing radiation, can exhibit properties excellent not only in flame retardance and mechanical strength but also in such properties as heat resistance, resistance to heat deformation, and resistance to chemicals.
The invention is described in more detail below.
The flame retardant resin composition according to the invention is basically obtained by compounding 100 parts by weight of thermoplastic resin with 100 to 250 parts by weight of metal hydroxide and either 5 to 50 parts by weight of acetate or 5 to 80 parts by weight of calcium carbonate.
The thermoplastic resins used as the base polymer of the flame retardant resin compositions can be cited by way of example and without limitation:
polyolefin, such as polyethylene and polypropylene;
ethylene-xcex1-olefin copolymer, such as ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-methacrylic acid copolymer, and ethylene-methyl acrylate copolymer;
thermoplastic elastomer such as polyolefin elastomer, including polyurethane elastomer, polyester elastomer, and ethylene-propylene copolymer elastomer, and polyamide elastomer; and
polyester such as polyethylene terephthalate and polybutylene terephthalate. One of the thermoplastic resins may be used singly or two or more of them may be used in combination.
One kind or two or more kinds of the above ethylene-xcex1-olefin copolymer selected from ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer, ethylene-methacrylic acid copolymer, and ethylene-methyl acrylate copolymer may be preferably used singly or in combination from the point of view of flame retardance, flexibility, and the like. The ethylene-vinyl acetate copolymer especially gives good results from the viewpoint of flame retardance and the like.
When the ethylene-vinyl acetate copolymer is used, that containing 6 to 50% by weight, or preferably 10 to 48% by weight, of vinyl acetate component can be used favorably from the point of view of the balance between mechanical strength and flame retardance. As to the melt fluidity, when the melt flow rate (at 190xc2x0 C. and under a load of 2.16 kg) is set within the range between 0.5 and 30, or preferably within the range between 0.5 and 20, favorable results can be obtained in view of extrusion workability and the like.
When the vinyl acetate content is less than 6% by weight, the flame retardance is decreased, and when it is more than 50% by weight, the mechanical strength is decreased.
Further, as to the melt flow rate of the ethylene-vinyl acetate copolymer, when it is less than 0.5, the surface of the extruded moldings tends to become rough and, when it is more than 30, the mechanical strength tends to decrease.
The conditions of the xcex1-olefin content and the melt flow rate as said of the ethylene-vinyl acetate copolymer above are correspondingly applicable to the other ethylene-xcex1-olefin copolymers.
In using the above ethylene-xcex1-olefin copolymer, ethylene unsaturated compound other than the above exemplified xcex1-olefin may be copolymerized according to need.
1) When an organosilicon compound coupling agent expressed as general formula [1]:
(where R denotes alkyl including acryl, methacryl, or allyl and Y 1 , Y 2, and Y3 denote atomic groups selected from the groups of alkyl, alkoxyl, and halogen) in the amount of 0.1 to 10 parts by weight is added to 100 parts by weight of the thermoplastic resin, favorable results can be obtained from the viewpoint of physical properties.
2) As examples of the silane coupling agent expressed as general formula [1],
xcex3-methacryloxypropyltrimethoxysilane,
xcex3-methacryloxypropyltriethoxysilane,
xcex3-acryloxypropyltrimethoxysilane,
xcex3-methacryloxypropyldimethoxymethylsilane, and
xcex3-methacryloxypropyldimethylchlorosilane may be cited, and one or a mixture of two or more of them may be used.
1) As examples of the metal hydroxide (a), magnesium hydroxide, calcium hydroxide, aluminum hydroxide, and the like can be cited. From the point of view of extrusion working temperature and the like of the resin composition, magnesium hydroxide and aluminum hydroxide are more preferably used.
As to the particle size of the used metal hydroxide (a), if that of 0.3 to 30 xcexcm, or preferably that of 0.5 to 25 xcexcm, in diameter and that of approximately 3 to 30 m2/g, or preferably that of 5 to 28 m2/g, in specific surface area by the BET method, is selected, satisfactory results can be obtained from the viewpoint of flame retardance, kneadability, extrusion workability, mechanical strength, and the like.
If the particle diameter of the metal hydroxide (a) is less than 0.3 xcexcm, particles tend to stick together resulting in the increase of the kneading time and, if it exceeds 30 xcexcm, the mechanical strength tends to decrease.
When the specific surface area of metal hydroxide (a) is less than 3 m2/g, the flame retardance tends to be lowered and, when it exceeds 30 m2/g, particles tend to readily stick together to prolong the kneading time.
2) Further, when the surface of the metal hydroxide (a) is treated with a surface treatment agent, good results can be obtained from the viewpoint of kneadability of the resin composition and elongation.
As examples of the surface treatment agent, anionic surface-active agents including fatty acid such as stearic acid and fatty acid metallic salt such as sodium stearate and sodium oleate can be cited.
3) Further, when the surface of the metal hydroxide is treated with an organosilicon compound coupling agent expressed as general formula [1], favorable results can be obtained from the viewpoint of physical property.
The acetate (b1) used in combination with the metal hydroxide (a) in this invention is basically a compound expressed as general formula Mn (CH3COO)n, where Mn denotes a cation whose valence is n.
As examples of the sa me, magnesium a cetate, sodium acetate, potassium acetate, zinc acetate, copper acetate, ferrous acetate, calcium acetate, aluminum acetate, nickel acetate, cobalt acetate, gallium acetate, silver acetate, tin acetate, barium acetate, cerium acetate, lead acetate, and beryllium acetate can be cited.
As types of salt of the acetate (b1), there are normal salt, acid salt, basic salt, and polynuclear metallic complex salt, some of which containing crystal water can also be used.
Of those mentioned above, magnesium acetate, sodium acetate, zinc acetate, copper acetate, ferrous acetate, calcium acetate, aluminum acetate, nickel acetate, and barium acetate can be favorably used from the viewpoint of extrusion working temperature of the resin composition and the like.
As to the particle diameter of the acetate (b 1), when that of 0.5 to 5 xcexcm, preferably that of 0.5 to 3 xcexcm, is selected, favorable results can be obtained from the viewpoint of not only the kneadability with the base polymer but also the melt extrusion workability when it is compounded with the base polymer to provide a resin composition. When the surface is treated with an anionic surface-active agent as with the metal hydroxide, such characteristics as the kneadability with the base polymer and the melt extrusion workability when made into a resin composition can be improved.
1) As examples of calcium carbonate (b2) to be used in combination with metal hydroxide (a) in this invention, heavy calcium carbonate obtained by pulverizing such as calcite, Iceland spar, aragonite, limestone, marble, and whiting, precipitated calcium carbonate as synthetic stone, and light calcium carbonate can be cited.
The crystal structure of the calcium carbonate (b2) takes on a rhombohedral calcite structure of a hexagonal system or an aragonite type structure of an orthorhombic system.
Synthetic calcium carbonate of the same, having uniform particle diameter distribution, is favorably used from the viewpoint of extrusion workability and physical properties.
As to the primary particle diameter of the calcium carbonate (b2), if that of not larger than 4 xcexcm and preferably that of not larger than 3 xcexcm, or more preferably not larger than 1 xcexcm, is selected, favorable results can be obtained from the viewpoint of flame retardance, kneadability with the base polymer, and the like.
2) Further, if one kind or a mixture of two or more kinds selected from the group of calcium carbonate (b2) whose surface is treated with a surface treatment agent of fatty acid type, oil and fat type, surface-active agent type, wax type, and the like, or that whose surface is treated with a coupling agent of silane type, titanate type, aluminum type, zirco-aluminum type, carboxylic acid type, phosphate type, and the like is used, such characteristics as kneadability can be improved with the base polymer and the melt extrusion workability when it is made into a resin composition.
1) As to the amount of metal hydroxide (a) and acetate (b1), or calcium carbonate (b2), to be compounded with the thermoplastic resin, favorable results are obtained from the viewpoint of flame retardance and mechanical strength when 100 to 250 parts by weight, or preferably 100 to 200 parts by weight, of metal hydroxide, in combination with 5 to 50 parts by weight, or preferably 10 to 40 parts by weight, of acetate, or with 5 to 80 parts by weight, or preferably 5 to 30 parts by weight, of calcium carbonate, were compounded with 100 parts by weight of the thermoplastic resin.
The flame retardance tends to deteriorate if the compounded amount of the metal hydroxide (a) is less than 100 parts by weight, regardless of the compounded amount of the acetate (b1) or that of the calcium carbonate (b2), and mechanical strength tends to decrease if the compounded amount of the metal hydroxide (a) exceeds 250 parts by weight.
Further, even if the compounded amount of the metal hydroxide (a) is within the range of 100 to 250 parts by weight, problems such as diminished flame retardance arise if the compounded amount of the acetate (b1) is less than 5 parts by weight or the compounded amount of the calcium carbonate (b2) is less than 5 parts by weight and that mechanical strength is decreased if the compounded amount of the acetate (b1) exceeds 50 parts by weight or the compounded amount of the calcium carbonate (b2) exceeds 80 parts by weight.
2) In the flame retardant resin composition of the invention, the drawback of the conventional thin-wall high-strength non-halogen insulating wires, tubes, heat-shrinkable tubes, or flat cables continuing to burn more than 20 seconds has been solved by mixing the thermoplastic resin with the acetate (b1) or calcium carbonate (b2) in an amount within a specific range, in addition to the metal hydroxide (a).
Further, it has also been found that, if the flame retardant resin composition is applied to the sheath for high voltage DC electric wire, the product can satisfy the vertical combustion test.
3) Mixing and Molding
In mixing the thermoplastic resin, the metal hydroxide, and the acetate or the calcium carbonate, a known mixing apparatus such as an open roll mixer, Bunbury mixer, pressure kneader, and biaxial mixer can be used.
From the thus obtained resin composition, various types of moldings for insulated wire, tube, heat-shrinkable tube, flat cable, high voltage DC electric wire, and the like can be easily produced by using a known resin molding apparatus for melt-extrusion and injection-molding.
1) The resin composition of the invention can, for the purpose of improving its characteristics, be mixed with various types of polymers such as EDPM and ethylene acrylic rubber within a range of an amount not impairing such characteristics as flame retardance and mechanical strength.
2) Further, various additives such as thermal stabilizer, antioxidant, ultraviolet absorber, lubricant, process stabilization auxiliary, coloring agent, foaming agent, reinforcing agent, organic or inorganic filler, and multifunctional monomer can be added to the resin composition.
3) The above multifunctional monomer, in particular, serves as a cross-linking assistant agent and, especially at the time of irradiation with ionizing radiation, improves the cross-linking effect. Hence, it may be added to the resin component according to need.
As examples of the multifunctional monomer, monomers containing plural portions of unsaturated linkage in the molecule such as trimethylolpropanetrimethacrylate, pentaerythritoltriacrylate, ethyleneglycoldimethacrylate, triallylcyanurate, and triallylisocyanurate can be cited.
When a flame retardant resin composition of the invention is extruded by the use of a melt extruder or the like onto a conductor to cover the same, the product can be used as it is as a flame retardant insulated wire or a flat cable free from the problem of generating harmful gases when it is burned.
Further, if the thus obtained flat cable is sandwiched between two sheets of insulating polymeric film such as polyester film, the product can be used as a flame retardant flat cable free from the problem of generating harmful gases when burned.
When the insulation is cross-linked by the method of subjecting the insulated wire or the flat cable to irradiation of ionizing radiation or the like, the insulated wire or the flat cable can be made into one that is excellent in such characteristics as mechanical strength, heat resistance, and resistance to heat deformation.
1) The conventional resin composition made to be flame retardant by having a thermoplastic resin such as polyolefin compounded with a large amount of magnesium hydroxide as halogen-free flame retardant has good flame retardance. However, since it has poor compatibility with the thermoplastic resin when it is applied to an insulated wire, its initial tensile strength becomes low and, further, the physical property is greatly deteriorated when it is heat aged. This invention can solve such problems more effectively.
2) The inventors developed earlier a thin-wall high-strength non-halogen insulated wire in conformity with the UL Standards. While this insulated wire satisfies the requirement of extinction of a flame within 60 seconds as provided in the VW-1 test, it sometimes continues to burn 20 seconds or more and, hence, it has not been a satisfactory thin-wall high-strength non-halogen insulated wire. Therefore, the development of a non-halogen flame retardant electric wire having higher flame retardance has been desired. This invention can also solve this problem.
3) The flame retardant resin composition of the invention, by virtue of the characteristic feature of its composition, can provide a thin-wall, high-strength, and high flame retardant non-halogen insulated wire.
That is, the invention provides a thin-wall high-strength non-halogen insulated wire with a conductor whose outer diameter is not larger than 1.0 mm, preferably between 0.1 and 1.0 mm, covered with a flame retardant resin composition, and with the insulation cross-linked and, especially, irradiated with ionizing radiation.
If the insulation layer of a wire is less than 0.1 mm in thickness, its normal withstand voltage is rendered unpractical and, if the insulation thickness is more than 1.0 mm, there arises a problem related to the flame retardance in the case of the wire having a fine conductor which is used for wiring within an appliance.
4) This thin-wall high-strength insulated wire is suitable as an insulated wire for wiring within an appliance, satisfying various safety regulations such as the UL Standards and it is advantageous in that, while securing safety against fire, it produces no environmental pollution.
The flame retardant resin composition of the invention can be made into an insulating tube by such a method as melt extrusion.
The tubular molding of the flame retardant resin composition of the invention can be processed into a heat-shrinkable tube, first, by cross-linking it, especially by irradiating it with ionizing radiation and, then, by expanding it in its radial direction by such a method as to send compressed air into it at a high temperature and thereupon cooling it so that it maintains its expanded form.
A high voltage DC electric wire excellent in such characteristics as mechanical strength, heat resistance, and resistance to heat deformation can be obtained by extruding an insulation layer made of an ethylene-xcex1-olefin copolymer resin composition on a conductor and then a jacketing made of the flame retardant resin composition of the invention thereon with a melt-extruder or the like, and further by cross-linking respective layers by applying an ionizing radiation or the like to them, and in particular by having a chemical cross-linking agent such as organic peroxide previously mixed in the insulation layer and the jacketing and by cross-linking each layer separately or both layers at the same time.
1) While electron beam, accelerated electron beam, gamma ray, beta ray, X-ray, alpha ray, ultraviolet ray, and the like can be cited as examples of the ionizing radiation, the accelerated electron beam can be used most favorably from the viewpoint of its industrial utilization, such as handiness of the beam source, the thickness penetrated by the ionizing radiation, and the speediness in the cross-linking process.
As to the exposure dose of the ionizing radiation, it is favorable when the electron beam, for example, is used, between 3 and 50 Mrad, or preferably between 5 and 25 Mrad.
If the exposure dose is under 3 Mrad, the effect of improving the tensile strength is a little and, if it is over 50 Mrad, the elongation is conversely decreased.
2) Instead of radiating with ionizing radiation, a chemical cross-linking method can also be used in which an organic peroxide or the like is previously mixed in the flame retardant resin composition and, after the extrusion, the product is heat treated.
As examples of the organic peroxide, dicumylperoxide, bis(t-butylperoxyisopropyl)peroxide, and the like can be cited.
However, irradiation with ionizing radiation is more preferable for satisfying both properties of the initial mechanical strength and the flame retardance.